A nonvolatile memory device having a rewritable nonvolatile memory is increasingly demanded mainly for a semiconductor memory card. The semiconductor memory card is high-price compared to an optical disk, a tape medium, and the like. The semiconductor memory card, however, is increasingly demanded as a recording medium for a portable apparatus such as a digital still camera and a mobile phone because of merits such as small-size, lightweight, vibration resistance, and easy handling, and is used for not only a consumer-use moving image recording apparatus but also a professional-use moving image recording apparatus. In addition, not only the portable apparatus but also a stationary apparatus such as a digital television and a DVD recorder include a slot for the semiconductor memory as standard equipment. Thus, still images shot with the digital still camera can be browsed on the digital television, and moving images shot with the consumer-use moving image recording apparatus can be dubbed to the DVD recorder.
The semiconductor memory card includes a flash memory as a nonvolatile main memory, and has a memory controller for controlling it. The memory controller controls data reading and data writing to the flash memory in accordance with data reading and data writing commands from an access device such as a digital still camera.
In these years, needs for a large capacity semiconductor memory card is grown to store AV contents of highly-improved quality such as a still image and a moving image, that is, a large capacity of data size of one content. According to this, when an AV content recorded in the semiconductor memory card is dubbed to a recording medium such as a hard disk or DVD recorder incorporated in a hard disk recorder and a personal computer, a performance able to read data from the semiconductor memory at a higher speed is required. In addition, when an AV content recorded in the recording medium such as the hard disk is dubbed to the semiconductor memory card, a performance able to write data to the semiconductor memory at a higher speed is required. That is, it becomes important from now to reduce a waiting time of user by dubbing the recorded data at a high speed between the recording medium.
Conventional techniques for controlling the high speed data reading and writing in the semiconductor memory card are: a technique of a parallel access of a flash memory shown in Patent document 1; and a technique for speeding up a bus to connect a semiconductor memory card to an access device shown in Patent document 2.
However, when data is read or written at a high speed, surface temperatures of a host device and a semiconductor memory card become exceedingly high in general, and thereby a user is at a risk of a burn when ejecting the semiconductor memory card from the host device. Patent document 3 discloses a conventional technique for detecting and controlling such heat generation. This technique prevents increase of temperature by detecting: a temperature of an MPU; and opening and closing conditions of a lid of a connector and by switching an operation clock of the MPU.    Patent document 1: Japanese Unexamined Patent Publication No. 2000-510634    Patent document 2: Japanese Unexamined Patent Publication No. 2003-223623    Patent document 3: Japanese Unexamined Patent Publication No. H09-237129